A torque detecting apparatus that is used in an electric power steering system (EPS) is designed to calculate a torque applied to an input shaft by detecting a torsional angle of a torsion bar which connects the input shaft to an output shaft.
Torque detecting apparatuses of this type have already been proposed in Patent Document 1 and Patent Document 2 below. Patent Document 1 describes a torque detecting apparatus in which an input shaft (a first shaft) and an output shaft (a second shaft) are connected together coaxially via a torsion bar (a connecting shaft). A cylindrical permanent magnet having a plurality of magnetic poles is fixed to the input shaft. Two annular magnetic yokes, which surround the permanent magnet, are fixed to the output shaft. Two magnetic flux concentrating rings are disposed around the circumference of each magnetic yoke which each have a magnetic flux concentrating portion for inducing a magnetic flux from the magnetic yoke and concentrating the induced magnetic flux. Additionally, two magnetic flux detectors are provided for detecting individually magnetic flux concentrated to each magnetic flux concentrating portion. Then, the torque applied to the input shaft is calculated based on an output signal from each magnetic flux detector.